Security is coming over in store (7)
I believe the answer is:
deposit
'security' is the definition.
(deposit is a kind of security)
'is coming over in store' is the wordplay.
'coming over' is a reversal indicator.
'in' indicates putting letters inside.
'store' becomes 'depot' ('depot' can be a synonym of 'store').
'is' backwards is 'si'.
'si' placed into 'depot' is 'DEPOSIT'.
(Other definitions for deposit that I've seen before include "Drop" , "part-payment" , "secure an item" , "fur, possibly" , "Sediment or bank lodgment" .)